1. Field of the Invention
The present invention relates to a mask assembly for color cathode ray tube (CRT). More particularly, the present invention is directed to a mask assembly for a color cathode ray tube, wherein an amount of tension applied to a shadow mask is reduced by preventing a main frame for applying tension in the shadow mask from deformation due to creeping during a high temperature process. An amount of tension is reduced by regulating the ratios of thickness, width, and height of the main frame to the thickness of shadow mask.
2. Description of the Related Art
FIG. 1 depicts a partial cross-section of structure of general color cathode ray tube (CRT). With reference to FIG. 1, the color CRT is a primary constitutional part by which an image is displayed in an image display apparatus such as a television monitor or a computer monitor. This CRT is composed of a panel 1 disposed at a front direction, and a funnel 2 disposed at the rear of the panel 1.
Also, within an inner space defined by said panel 1 and funnel 2, the CRT further comprises a fluorescent surface 4 emitting a fluorescence light, an electron gun embedded in a neck part of said funnel 2 for producing an electron beam 6 impinging on said fluorescent surface 4, a shadow mask 3 for discriminating a color which the fluorescent surface 4 finally fluoresces to create, a frame composed of a main frame 7 applying tension to the shadow mask 3 and a sub-frame 15 supporting said main frame 7, a spring 9 disposed at the side of said main frame for coupling said frame to said panel 1, an inner shield 8 fixed by welding to said sub-frame 15 for shielding an external earth magnetic field, and a reinforcing band 12 disposed at the side peripheral of said panel 1 for withstanding external impacts.
Also, the CRT further comprises a deflection yoke 5 for deflecting the electron beam 6 discharged at the electron gun (not shown) to upward or downward and left or right, and 2,4,6 pole magnets 11 for directing a trajectory of the beam into certain fluorescence materials, thereby preventing a deterioration of color purity.
The operational principle of the color cathode ray tube depicted in FIG. 1 is described below. The electron beam 6 discharged at the electron gun embedded in the neck of panel 2 strikes the fluorescent surface 4 formed in the inner side of panel 1 by the anode voltage applied to the cathode ray tube. This electron beam is deflected by the deflection yoke 5 upward or downward and also right or left prior to arriving to the fluorescent surface 4, thereby forming a pixel.
This cathode ray tube is in a high vacuum state so that a firecracker phenomenon can occur easily in the event of an external impact. Therefore, panel 1 is designed to have a structure strength that can withstand atmospheric pressure so as to prevent this phenomena.
Also, impact-resistance capability is guaranteed in such a way that stress experienced by a cathode ray tube in the high vacuum state is distributed with the reinforcing band 12 mounted at the outer surface of the skirt of panel 1.
The shadow mask 3 and main frame 7 are made to be in an equilibrium state by deformation when the main frame 7 for applying a tension to the shadow mask is welded.
In this case, a stress which is applied to the main frame 7 for applying tension to the shadow mask 3 should be lower than a material""s breakdown strength so that a problem related to rigidity does not arise.
Meanwhile, if the stress applied to said main frame 7 is lower than a material""s breakdown strength, no problem is arises with respect to rigidity, but a problem of a tension reduction phenomena in the shadow mask occurs by deformation created by creeping during a high temperature thermal process.
Accordingly, the present invention has an objective of providing a mask assembly of a cathode ray tube which prevents the reduction of tension in the shadow mask produced by the deformation of the main frame due to creeping during a high temperature thermal process, with the ratios of thickness, width and height of the main frame to the thickness of shadow mask regulated.
In a preferred embodiment for achieving an objective of the present invention, a relation of T/txe2x89xa745 is satisfied, where the thickness of shadow mask is t and the thickness of a part where a main frame is welded to a shadow mask is T, for a cathode ray tube comprising a panel having a fluorescent surface disposed at an inner side thereof, a funnel adhered to a rear side of said panel, wherein adhesion is enabled by frit glass, a shadow mask coupled to the inner side of said panel, wherein a plurality of electron through-holes perform color discrimination for an electron beam, and a frame composed of a main frame welded to the shadow mask for supporting said shadow mask toward the panel and a sub-frame supporting said main frame.
In another preferred embodiment of the present invention a relation of W/txe2x89xa7270 is satisfied, where a thickness of a shadow mask is t and a width of a part attached to a sub-frame of a frame is W, for a cathode ray tube comprising a panel having a fluorescent surface is disposed at an inner side thereof, a funnel adhered to a rear side of said panel wherein adhesion is enabled by frit glass, the shadow mask coupled to the inner side of said panel, wherein a plurality of electron through-holes perform color discrimination for an electron beam, and a frame composed of a main frame welded to the shadow mask for supporting said shadow mask to the panel and the sub-frame supporting said main frame.
In another preferred embodiment of the present invention a relation of H/txe2x89xa7270 is satisfied, where a thickness of shadow mask is t and a length of a main frame from said shadow mask to a sub-frame is H, for a cathode ray tube comprising a panel having a fluorescent surface disposed at an inner side thereof, a funnel adhered to a rear side of said panel wherein adhesion to said panel is enabled by frit glass, the shadow mask coupled to the inner side of said panel, wherein a plurality of electron through-holes perform color discrimination for an electron beam, and a frame composed of a main frame welded to the shadow mask for supporting said shadow mask to the panel and the sub-frame supporting said main frame.
In another preferred embodiment of the present invention the main frame to which said shadow mask is welded is below 72% of a high temperature breakdown strength and also below 65% of a room temperature breakdown strength, for a cathode ray tube comprising a panel having a fluorescent surface disposed at an inner side thereof, a funnel adhered to the rear side of said panel wherein adhesion to said panel is enabled by frit glass, the shadow mask coupled to the inner side of said panel, wherein a plurality of electron through-holes perform color discrimination for an electron beam, and a frame composed of a main frame welded to the shadow mask for supporting said shadow mask to the panel and the sub-frame supporting said main frame.